1. Field of the Invention
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of reducing secondary defect formation due to indium halo doping in the fabrication of integrated circuits.
2. Description of the Prior Art
Halo or pocket implants are made in the fabrication of integrated circuits in order to suppress n-channel and p-channel short channel effects, to suppress drain-induced-barrier-lowering, and to suppress high electrical field regions that could cause punchthrough phenomenon. The use of heavy ions (e.g. antimony or indium) as a dopant for the halo pocket of the nMOSFET becomes more important with the shrinkage of the nMOS transistor to below the sub-0.1 μm regime. See “Optimum Halo Structure for Sub-0.1 μm CMOSFETs”, Wen-Kuan Yeh, IEEE Transaction on Electron Devices, Vol. 48, No. 10, October 2001 and “Antimony Assisted Arsenic S/D Engineering for sub-0.1 μm nMOSFETs: A Novel approach to steep and retrograde indium pocket profiles,” Howard C. H. Wang, IEDM 2001.
Indium, as a heavy ion, allows implantation to be carried out at higher energy with smaller profile spread, providing better process control. The indium ion has large cross-sectional area and, when implanted at high energy, causes much damage to the silicon lattices compared to its boron counterpart. (See “Effect of End of Range on transient Enhanced Diffusion of Indium Implanted in Silicon”, T. Noda, Journal of Applied Physics, Vol. 88, No. 9, 1 Nov. 2001. ) This causes formation of the End of Range (EOR) secondary defect at the tail end of the profile upon insufficient annealing. A prolonged soak anneal would cause unnecessary dopant diffusion, undesirable for shallow junction formation. EOR defects when present in the depletion region of the PN junction cause severe junction leakage. Additional issues related to the indium ion include low dopant activation (see “Enhanced electrical activation of indium coimplanted with carbon in a silicon substrate”, H. Noudinov, Journal of Applied Physics, Vol. 86, No. 10, p. 5909, 15 Nov. 1999) and transient enhanced diffusion (TED) (see “Indium Transient Enhanced Diffusion”, P. B. Griffin, Applied Physics Letters, Vol. 73, No 20, p. 2986, 16 Nov. 1998 and “Evolution of end of range damage and transient enhanced diffusion of indium in silicon”, T. Noda, Journal of Applied Physics, Vol. 91, No. 2, p. 639, 15 Jan. 2002).
Reports have shown that with the incorporation of carbon into the amorphous-crystalline silicon interface of the dopant implant profile, EOR secondary defects can be removed. This interface is an area or region at the tail end of the implant profile which maintains its crystalline property, but it is saturated with the dopant impurity. (See “Elimination of secondary defects in preamorphized Si by C+ implantation”, Satoshi Nishikawa, Applied Physics Letters, 62(3), 18 Jan. 1993 and “Removal of end of range defect in Ge+ pre-amorphized Si by carbon ion implantation”, Peng-Shiu Chen, Journal of Applied Physics, Vol. 85, No. 6, 15 Mar. 1999). A common method of introducing carbon into the amorphous-crystalline silicon is through carbon co-implantation with dopant ions. Substitutional carbon was shown to act as a sink for silicon interstitials formed, preventing the clustering of silicon interstitials, thereby preventing EOR secondary defect formation. (See “Suppression of dislocation formation in silicon by carbon implantation”, T. W. Simpson, Applied Physics Letters, 67(19), 6 Nov. 1995). The implantation of carbon itself introduces additional silicon interstitials, reducing the effectiveness of carbon as a sink.
U.S. Pat. 6,541,829 to Nishinohara et al. discloses an indium halo implant. U.S. Pat. No. 6,514,886 to U'Ren teaches an RPCVD method prior to epitaxy.